1. Field of the Invention
The present invention generally relates to systems and methods for creating analog signals to produce sound.
2. Description of Related Art
Many systems exist for creating an automobile chime in response to an event. Different sounding chimes are provided for events such as seatbelt unbuckled, driver door open, key in ignition. Prior art systems use a control circuit to interpret events and associate the event with a signal having a prescribed amplitude and frequency corresponding to a particular sound of chime. The control circuit communicates the signal to a pulse width modulator. The pulse width modulator creates an electrical signal corresponding to the sound of the chime. The electrical signal is amplified and communicated to a speaker to synthesize the chime. However, the chime is monotone due to circuit design and the limited bandwidth of the pulse width modulator. Improvements have been made to existing systems by introducing a decaying factor to vary the tone of the chime. However, the chimes are still synthetic and similar in tone due to the limited bandwidth of the pulse width modulator.
In view of the above, it is apparent that there exists a need for a system for producing automobile chimes with improved band width over the prior art designs.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, in an embodiment of the present invention a system for creating an analog signal to produce a sound using a precision multiple pulse width modulator circuit is provided.
In an embodiment of the present invention, the system includes a control circuit, a pulse width modulation circuit, and a mixer circuit. The control circuit includes a memory for storing sound tables. The control circuit senses an event, accesses the sound table associated with the event, retrieves an entry value from the sound table, and communicates the entry value with the pulse width modulation circuit. The pulse width modulation circuit includes (I) number of pulse width modulators and the entry value is represented by a number having (I) places where each pulse width modulator represents a place of the number representing the entry value.
The mixer circuit includes multiple resistors. Each resistor is connected to a pulse width modulator from the pulse width modulation circuit on one end and the common node of the mixing circuit on the other end. The resistors have the effect of scaling the signal from each pulse width modulator thereby creating an analog signal at the common node corresponding to the entry value of the sound table.
In yet another embodiment of the present invention a low pass filter circuit is provided. The low pass filter reduces noise in the analog signal from the common node and in an audio amplifier circuit. Accordingly, the analog signal is appropriately scaled before reaching the audio output device.
The sound tables can store data corresponding to high fidelity chimes such as music or even voice. The use of the precision multiple pulse width modulator circuit according to the present invention provides the additional band width to produce the high fidelity chimes without significantly impacting the cost of the system.
Further aspects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.